Figure 6.

Mechanism of action of NTD-specific neutralizing mAbs

(A) Competition of S2L28, S2M28, S2X28, and S2X333 with ACE2 to bind to SARS-CoV-2 S as measured by biolayer interferometry. ACE2 was immobilized at the surface of the biosensors before incubation with the S ectodomain trimer alone or pre-complexed with mAbs. The vertical dashed line indicates the start of the association of free S or S/mAb complexes with solid-phase ACE2. The anti-RBD S2E12 mAb was included as positive control.

(B) mAb-mediated S₁ subunit shedding from cell surface expressed SARS-CoV-2 S as determined by flow cytometry. The anti-RBD S2M11 and S2E12 mAbs were included as negative and positive controls, respectively.

(C) Neutralization of authentic SARS-CoV-2 (SARS-CoV-2-Nluc) by S2L28, S2M28, S2X28, and S2X333 IgG or Fab. S309 and S2M11 Fab and IgG were also included as controls. Symbols are means ± SD of triplicates. Dotted lines indicate IC₅₀ and IC₉₀ values.

(D) SPR analysis of mAbs binding to the SARS-CoV-2 S ectodomain trimer. Gray dashed line indicates a fit to a 1:1 binding model. The equilibrium dissociation constants (K_D) or apparent equilibrium dissociation constants (K_D, app) are indicated. White and gray stripes indicate association and dissociation phases, respectively.

(E and F) Activation of FcγRIIa H131 (E) and FcγRIIIa V158 (F) induced by NTD-specific mAbs. The anti-RBD mAb S309 was included as positive control. One independent experiment out of at least two is shown.

See also Figures S1 and S5 and Table S1.